The ability of phytohemagglutinins (PHA) from plant sources to transform normal lymphocytes is thought to be a phenomenon involving the plasma membrane. The PHA isolated from the common lentil (LCH) possesses the ability to bind glycoproteins containing mannosyl residues as well as this transforming ability. To study this phenomenon, plasma membranes were isolated from lymphocytes in long term culture. A step gradient of polyethylene glycol-dextran was used for membrane isolation and 5'-nucleotidase was used as a marker to follow purification. Membranes were solubilized using 0.25% deoxycholate and passed over an affinity column of LCH-Sepharose. Three fractions could be eluted from column: a hetergeneous glycoprotein fraction (HGP) and two fractions eluted with high salt (HSI & HSII). HGP was eluted from the column with 4% alpha-methylmannodide (MeMan) and contained seven proteins by SDS polyacrylamide gel electrophoresis (PAGE), with high molecular weights ranging from 24,000 to 94,000. Greater than 90% of the protein of this fraction was eluted in the void volume of a Sephadex G-100 column using 4% MeMan in 1M NaC1. HSI appeared homogeneous on SDS-PAGE (Mw 86,000). When HSI was re-applied to the affinity column, it was not bound. HSII was also found to be homogeneous on SDS-PAGE (Me 29,000). This fraction was found to bind to the affinity column upon reapplication. Supported in part by USPHS Grant CA 14351-01.